Oligonucleotide conjugates have been extensively evaluated for use in siRNAs, where they are considered essential in order to obtain sufficient in vivo potency. For example, see WO2004/044141 refers to modified oligomeric compounds that modulate gene expression via an RNA interference pathway. The oligomeric compounds include one or more conjugate moieties that can modify or enhance the pharmacokinetic and pharmacodynamic properties of the attached oligomeric compound.
In contrast, single stranded antisense oligonucleotides are typically administered therapeutically without conjugation or formulation. The main target tissues for antisense oligonucleotides are the liver and the kidney, although a wide range of other tissues are also accessible by the antisense modality, including lymph node, spleen, bone marrow.
WO2008/113832 discloses LNA phosphorothioate gapmer oligonucleotides where the flanking regions comprise at least one phosphodiester between or adjacent to a LNA nucleoside. The oligomers were preferentially targeted to the kidney.
WO2004/087931 refers to oligonucleotides comprising an acid cleavable hydrophilic polymer (PEG) conjugate.
WO 2005/086775 refers to targeted delivery of therapeutic agents to specific organs using a therapeutic chemical moiety, a cleavable linker and a labeling domain. The cleavable linker may be, for example, a disulfide group, a peptide or a restriction enzyme cleavable oligonucleotide domain.
WO 2009/126933 refers to specific delivery of siRNA nucleic acids by combining targeting ligands with endosomolytic components.
WO 2011/126937 refers to targeted intracellular delivery of oligonucleotides via conjugation with small molecule ligands.
WO2009/025669 refers to polymeric (polyethylene glycol) linkers containing pyridyl disulphide moieties. See also Zhao et al., Bioconjugate Chem. 2005 16 758-766.
Chaltin et al., Bioconjugate Chem. 2005 16 827-836 reports on cholesterol modified mono- di- and tetrameric oligonucleotides used to incorporate antisense oligonucleotides into cationic liposomes, to produce a dendrimeric delivery system. Cholesterol is conjugated to the oligonucleotides via a lysine linker.
Other non-cleavable cholesterol conjugates have been used to target siRNAs and antagomirs to the liver—see for example, Soutscheck et al., Nature 2004 vol. 432 173-178 and Krützfeldt et al., Nature 2005 vol 438, 685-689. For the partially phosphorothiolated siRNAs and antagomirs, the use of cholesterol as a liver targeting entity was found to be essential for in vivo activity.
The present invention is based upon the discovery that highly effective targeted delivery of oligonucleotides is achieved by the use of a homing device linked to the oligonucleotide by means of a short region of nuclease labile nucleosides, such as phosphodiester linked DNA or RNA nucleosides.